Method of making cylindrical fuse

ABSTRACT

A method for producing electric power fuses comprising the steps of preparing two circular discs each having a central hole and a plurality of peripheral slits, and each slit having a lug at the radially inner end thereof, placing the circular discs at a predetermined distance, inserting fuse elements in the slits so that two ends of the fuse elements are fixed around the lugs, slipping an insulating tube over the fuse elements thus assembled, and filling the interior of the insulating tube with an arc extinguishing substance.

Unite States 36113 1191 1111 3,777,370 Wakui Dec. 11, 1973 [54] METHOD OF MAKING CYLINDRICAL 3,319,027 5/1967 Hitchcock 29/623 x FUSE 3,333,336 8/1967 Cameron et al. 29/623 3,371,410 3/1968 Gintout 29/623 X Invenwrr Toshio Wakui, Kawasaki-811i, 3,636,491 1/1972 Cameron 337/161 x Kanagawa-ken, Japan [73] Assignee: Fuji Denki Seizo Kabushiki Kaisha, Primary Emmi' er chafles Lanham Kawasakrshi Kanagawwken, Assistant ExammerV. A. DiPalma Japan Attorney-John C. Holman et al.

[22] Filed: Feb. 4, 1972 57 TR C [21] Appl. No.: 223,495 -A method for producing electric power fuses comprising the steps of preparing two circular discs each havl n ing a central hole and a plurality of perlpheral slits, g 3 29/623 g 6 Z 3; and each slit having a lug at the rad1ally inner end [58] Fie'ld 337/228 thereof, placing the circular discs at a predetermined 292 distance, inserting fuse elements in the slits so that two ends of the fuse elements are fixed around the lugs, li ing an insulating tube over the fuse elements thus [56] References Cited S pp 7 v assembled, and fillrng the 1nter1or of the msulatmg UNITED STATES PATENTS tube with an arc extinguishing substance. 2,209,823 7/1940 Lohausen 337/293 X 2,828,390 3/1958 McAlister... 4 Clam, 9 D'awmg 3,116,389 12/1963 Withers 337/293 X PATENTED DEC 1 1 I975 SHEET 2 [If 3 0 00m noon DON 1 METHOD OF MAKING CYLINDRICAL FUSE BACKGROUND OF THE INVENTION This invention relates generally to enclosed type power fuses and more particularly to an improved method through which power fuses of such an organization can be assembled efficiently.

Heretofore, users of power fuses, especially of those employable in electric power transmission and distribution systems of voltages higher than 3,000 V, are exerting much effort in acquiring power fuses of high current-limiting characteristics, accurate currentinterrupting capacities, and of uniform and reliable qualities, while the manufacturers of the power fuses are endeavoring to produce products of guaranteed excellent current-interrupting characterestics at low production cost.

In the production of electric power fuses of more than 3KV, certain points and factors as set forth in the following paragraphs (1) through (4) should be taken into consideration.

1. As for the fuse elements, there are two kinds, one being punched out of a flat Ag or Cu plate, and the other being of a wire form made of Ag or Cu.

Altough the former flat elements are economical in manufacture, the current-interrupting characteristics thereof at a high potential are not suff ciently good, and elements of this type are solely employed for lowvoltage use.

Since the high tension power fuses should have sufficiently high currentlimiting characteristics, nevertheless maintaining a sufficient interpolar insulating distance after the fusion of the fuse elements, wire-formed fuse elements having a relatively small cross-sectional area are employed, and the number of the fuse elements connected in parallel is selected to suit the rated current of the power fuse. The superiority of such a practice has been widely recognized after numerous experiments. Furthermore, a method to fabricate each fuse element in a spiral form and enclosing such elements in a porcelain tube for elongating the interpolar distance has also been known. However, manufacture of the spiral fuse elements has been found to be rather difficult.

2. According to my investigation, the length and diameter of the porcelain tube used for the power fuse of different voltage and current are as shown in the following table. Considering the fact that the greater part of the material cost of a power fuse depends on the size of the porcelain tube and the fact that the space required for the power fuse in a high tension power switchboard is of a limited nature, it is apparent that the length and diameter of the porcelain tube must be minimized as far as possible.

Each element consists of an Ag wire 0.] to 0.5 mm diameter would into a coil of 5 mm outer diameter,

3. Assembling of the fuse elements:

Two types are considered in the construction of spirally wound (or coiled) fuse elements. One is constructed in the form of a coreless type, and the other is constructed to have a core. Since the latter type of the construction lowers the utility factor of the inside space of the porcelain tube, the former type of the construction is mostly used in high tension power fuses.

However, when the spiral fuse elements of the coreless type are employed in a porcelain tube of the power fuse, extreme care must be exercised so as to place the fuse elements correctly without causing any entanglement between them. This, on the other hand, requires skilled workers, and the yield of the production of the power fuses also has not been satisfactory.

4. Quality control:

Because of the above described difficulty in assembling the fuse elements, X-ray tests have been conducted on some of the power fuses sampled from a predetermined number of completed power fuses. However, it is apparent that such a procedure requires a considerable additional cost, and hence raises the ultimate price of the power fuses.

SUMMARY OE THE INVENTION Therefore, a primary object of the present invention is to provide a novel method for producing electric power fuses of the above described nature without requiring any skilled personal technique.

Another object of this invention is to provide a novel method for producing electric power fuses, whereby the production cost of the power fuses can be substantially reduced.

Still another object of the invention is to provide a novel method for producing electric power fuses, whereby the,yield of the production can be substantially elevated.

A first step comprising preparing two circular discs of different diameters, each circular disc having a control square hole, a plurality of slits cut radially in a spaced apart relationship along the periphery of the circular disc so as not to reach the central square hole, and a plurality of lugs formed by folding the disc material outwardly at the inward bottom of each of the slits,

- and disposing the two circular discs thus prepared in a coaxially opposed but spaced apart relationship by means of an assembling jig so that each of the corresponding slits in the circular discs are aligned along the length of the assembling jig;

A second step of inserting a fuse element in each pair of the aligned slits of the two circular discs with both ends of the fuse element being fixed around the lugs provided at the bottoms of the slits;

A third step of rotating the jig intermittently around the longitudinal axis of the jig;

A fourth step of slipping over the fuse elements thus assembled a separately prepared insulating tube made of an inorganic, heat-resistant ceramic material and having cylindrical cap-shaped terminals at both ends of the insulating tube;

A fifth step of removing the jig out of the fuse assembly after the circular discs and the cylindrical capshaped terminals have been welded together, respectively;

A sixth step of filling the interior space of the insulating tube with an arc extinguishing substance through one of the square holes which is left open after the jig has been removed; and

A seventh step comprising welding end caps to both ends of the cylindrical cap-like terminals after the interior of the insulating tube has been filled by the arc extinguishing substance.

The nature, principle, and the utility. of the present invention will be more clearly understood from the following detailed description of the invention when read in conjunction with the accompanying drawings wherein like parts are designated by like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1(A) is a longitudinal sectional view of a conventional cylindrical fuse wherein the fuse elements are being assembled;

FIG. 1(B) is an end view of the fuse shown in FIG.

FIG. 2(A) is a longitudinal sectional view of an insulating ceramic tube onthe two ends of which are slipped cylindrical cap-shaped terminals;

FIG. 2(B) is a right-hand end view of the insulating ceramic tube with cylindrical cap-shaped terminals;

FIG. 3(A) is a side view of fuse elements partly assembled on two circular discs;

FIG. 3(B) is a right-hand end view of the partial assembly of FIG. 3(A) wherein elements other than the right-hand side circular disc are omitted for clarity of the view;

FIG. 3(C) is an enlarged sectional view showing a part of the circular disc shown in FIGS. 3(A) and 3(B); and

FIGS. 4(A) and 4 (B) are a longitudinal sectional view and a right-hand end view, with an end cover 300a removed, of a tubular, high tension, power fuse according to the present invention.

DETAILED DESCRIPTION As conducive to a full understanding of the present invention, a conventional method for assembling the fuse will first be described with reference to FIGS. 1(A) and 1(B). As is apparent from these figures, a hollow ceramic tube 1 provided with two cylindrical capshaped terminals 2a and 2b on two ends of the tube 1 is mounted on a freely rotatable working frame 3. The two cap-shaped terminals 2a and 2b are provided respectively with central holes 4 of the same diameter qb. On the outer surfaces of the cap-shaped terminals 2a, 2b, jigs 7a and 7b are attached respectively for fixing temporarily two ends of fuse elements 6 (only one of the fuse elements is indicated for simplification of the drawing).

When the fuse elements are assembled, a needle or wire is passed through one of holes 4a, also provided around the central hole 4 of the diameter 11 in a direction as designated by an arrow mark A, and the tip thereof is directed through the central hole 4 of the diameter (1) provided in the cap-shaped terminal 2b. Then, one end 6a of a fuse element 6 wound in the form of a hollow spiral is caught by the tip of the needle 5, and the fuse element 6 is introduced into the ceramic tube 1 while the other end 6b of the element is supported by a hand of the assembling worker. When the end 6a of the element is pulled-out to the right side of the hole 4a, the end 6a is temporarily fixed on a projection of the jig 7, and the other end 6b of the fuse element 6 is picked, for instance, with a pincette and inserted through a corresponding hole 4b provided in the other cylindrical cap-shaped terminal 2b from the right side to the left side. The end 6b of the element thus passed through the hole 4b is temporarily stopped on a projection of the jig 7b on the left-side, cap-shaped terminal 2b.

A desired number of the fuse elements are assembled inside of the ceramic tube by repeating the above described procedure. It will be apparent that the assembling work of the fuse elements becomes increasingly more difficult in accordance with an increase in the fuse elements. In fact, it has required highly skilled labor to avoid entanglement of these fuse elements when their number increases, and even with skilled labor, the occurrence of defective products has been higher than 15 percent.

The method for producing the high tension power fuses and a construction of the power fuses according to this invention will now be described with reference to FIGS. 2 through 4.

In FIGS. 2(A) and 2(B), there is shown an insulating tube 1 made of an inorganic, heat-resistant ceramic, on the two ends of which are fixed, by means of an adhesive, two cylindrical cap-shaped terminals 2a, 2b made of an electrically conductive material such as copper or copper alloy. The cap-shaped terminals 2a and 2b are provided with central holes I-Ia and Hb of diameters dla and dlb, respectively. The insulating ceramic tube 1 with the cap-shaped terminals 2a and 2b of the above described construction is employed after fuse elements are assembled as will be described hereinbelow for covering the fuse-element assembly. a

The assembling procedure of the fuse elements will now be described with reference to FIGS. 3(A), 3(B), and 3(C).

In these figures, there are shown two circular discs 11a and 11b made of an electrically conductive material such as copper or copper alloy and having diameters d2a and d2b, respectively. The circular discs Ila and 11b respectively have central square holes Sa and Sb of different sizes, and each of the circular discs 11a and 11b is provided with a plurality of radial slits 9 cut from the peripheral edge of the circular disc but not reaching the central square hole as shown in FIG. 3(B). The material of the circular disc is bent back outwardly at the radially inner end of each of the slits so that a lug 10 is thereby formed on each of the slits 9. In FIG. 3(C), one of such lugs 10 on the circular disc 11b is indicated as an example. The relation between the diameters d2a, d2b of the circular discs and the diameters dla, dlb of the holes in the cylindrical cap-shaped terminals 2a and 2b is so selected that The procedure of assembling the fuse elements is as follows. The circular disc terminals 11a, 11b are slipped over a specific jig in the form of a shaft 12 (indicated in FIG. 3 by oblique shading lines) which has portions adapted to be forced into the square holes Sa and Sb of the circular disc terminals 11a, 11b.

More specifically, a circular disc 11a having a larger diameter d2a is first slipped over the shaft 12, from the leftward end thereof, until the circular disc 11a abuts against a right-hand side step delimiting a first portion of the shaft 12 adapted to be engaged with the square hole Sa of the disc 11a, and then another circular disc 11b having a smaller diameter d2b is slipped onto the shaft 12 from the same end until the circular disc 11b abuts the second step delimiting a portion of the shaft 12 adapted to be engaged with the square hole Sb of the disc 11b. With such an arrangement, the distance between the two circular discs can be automatically made equal to the distance between the two cylindrical cupshaped terminals.

Furthermore, the two square holes Sn and Sb of the circular discs 11a and 11b are similar figures, and the positions of the slits 9 relative to the corners of the square hole Sa or Sb are also definitely determined. As a result, when the two circular discs 11a and 11b are mounted as described above on the shaft 12, the slits 9 and 9 on these circular discs are disposed in alignment along the longitudinal direction of the shaft 12.

While an example of a circular disc having eight slits equally spaced apart from each other and forming an equal angle 6 around the center thereof is illustrated in FIG. 3(B), the number of the slits is determined solely by the number of the fuse elements 6 to be connected in parallel within the tube 1. Furthermore, while the portions of the shaft 12 engaging with the square holes Sa and Sb of the circular discs 11 a and 11b are made with square cross sections conforming to the square holes Sn and Sb, the portions of the shaft 12 at the two ends thereof supported by the rotatable working frame 3 are made with circular cross sections, whereby the shaft 12 can be easily rotated about its longitudinal axis.

In FIG. 3(A), three fuse elements 6-1, 6-2, and 6-3 are shown to have been attached to the circular discs 11a and 11b. After completion of the attachment of the fuse element 6-3, the shaft 12 is rotated by a driving device (not shown) intermittently in the arrow direction until the succeeding pair of slits 9 are brought into the uppermost position. That is, the shaft 12 is rotated intermittently through increments of angle 0 around its longitudinal axis.

Then the fourth fuse element 6-4 is inserted into the slits now brought into the uppermost position, and the two ends thereof 6a and 6b are secured around the lugs corresponding to said fuse element 6-4.

Since each of the elements 6 contains a hollow helical portion, it has resilience along its length, and also since the lugs 10 are made to have a height of about 3 mm., the elements 6 can be attached to the lugs easily without requiring the application of any excessive force which might reduce or deform the cross-sectional area of the fuse element.

Furthermore, as shown in the drawing, two ends 6a and 6b of each fuse element 6 are formed beforehand into loops. This can be accomplished by colding the end portion of the wire-formed fuse element back for a suitable length with a portion of the wire to be formed into the loop being rounded through a rounding device (not shown), and the folded back portion of the wire being wound around the mating portion of the fuse element. In the course of the assembling of the fuse elements, the looped portions of the fuse elements are merely passed around the lugs, and after completion of the assembling, all of the portions of the fuse elements passed around the lugs may be soldered in one step.

By the above described procedure, a required number of fuse elements can be assembled outside of the insulating tube 1, whereby the work time required for the assembling of the fuse elements and the occurrence of unsatisfactory products can both be minimized, and the reliance upon skilled workers can be much reduced.

Additionally, because of the employment of the looped ends of the fuse elements, the possibility of the fuse elements being pulled within the insulating tube during the soldering process or actual use and defective operation of the power fuses can be substantially eliminated.

After the completion of the work of assembling the fuse elements, an insulating tube 1 as shown in FlG. 2 is slipped over the fuse elements. In this case, the cylindrical cap-shaped terminal 2a having a hole Ha of a larger diameter is first slipped over the circular disc 1 1b of a smaller diameter of the fuse-element assembly, and then the insulating tube 1 is advanced toward the circular disc 11a of a greater diameter. Because of the hereinbefore described relationship between the diameters, 1.e.,

ultimately, the forward end 20a of the cap-shaped terminal 2a abuts against the rearward surface of the circular disc 11a having a larger diameter d2a, and the inner surface of the end portion 20b of the cap-shaped terminal 2b abuts against the rearward surface of the circular disc 11b having a smaller diameter d2b as clearly shown in FIG. 4(A). At this instant, the periphery of the circular disc 11a and the end portion 20a of the cap-shaped terminal 2a are brazed together as indicated at 30a, and the inner periphery of the hole Hb through the end portion 20b and the rearward surface of the circular disc 1 1b are brazed together as indicated at 30b. The shaft 12 is pulled out of the assembly after completion of the above described brazing steps.

An end cover, for example, 300b is then secured by brazing over the end portion 20b, so that the square hole Sb formed through the circular disc 11b is thereby closed. An arc extinguishing substance such as silica is then poured through the square hole Sa while vibration is applied to the insulating tube 1. When the interior of the insulating tube 1 is sufficiently filled with the arc extinguishing substance, the other end cover, for example, 300a is secured by brazing over the end portion 20a so that the square hole Sa is thereby closed.

Although the present invention has been described with respect to preferred embodiment thereof, it will be apparent to those skilled in the art that various modifications and alterations may be carried out thereon without departing from the spirit and scope of the invention. For instance, the shape and construction of the cylindrical cap-shaped terminals, square holes of the circular discs, slits and pawls of the same, etc., may be modified in various ways, and the fuse elements themselves may be changed to the straight wire type instead of the above described hollow helical construction. Furthermore, the rotatable working frame 3 in FIG. 3(A) may be omitted if the shaft 12 is vertically supported with the circular disc 11a of a larger diameter placed downward and the circular disc 11b of a smaller diameter placed upward.

According to the present invention, since the depth of the slits in the circular discs may be suitably varied from each other, and the distance between each of the fuse elements may also be varied over a wide range,

with a minimum value of about 5 mm, the number of the fuse elements contained in the insulating tube 1 can be varied in a wide range, whereby the rated value of the fuse unit may be changed as'desired with the size of the insulating tube held at a minimum number of variations.

I claim:

1. A method for producing electric power fuses comprising l. a step comprising preparing two circular discs of different diameters, each disc having a central square hole, a plurality of slits cut radially in a spaced apart relation along the periphery of the disc but not reaching the central square hole, and a plurality of lugs formed by bending the disc material outwardly at the inner bottom of each of the slits, and disposing the two discs thus prepared in an opposed but spaced apart relationship by an assembling jig having a longitudinal axis so that each of corresponding slits in the two circular discs are aligned along the longitudinal direction of the assembling jig;

2. a step of inserting each of fuse elements into a respective pair of the aligned slits in the two discs, with both ends of the fuse element being fixed around the lugs provided at the bottoms of the corresponding slits;

3. a step of rotating the jig intermittently around the longitudinal axis of the jig;

4. a step of enclosing the fuse elements thus assembled within an insulating tube made of an inorganic, heat-resistant, ceramic material and having cylindrical cap-shaped terminals at both ends of the insulating tube;

5. a step of removing the jig out of thefuse assembly after the discs and the cylindrical cap shaped terminals have been brazed together, respectively;

6. a step of filling the interior space of the insulating tube with an arc extinguishing substance through one of the square holes which is left open after the jig has been removed; and

7. a step comprising securing by brazing end caps to both ends of the cylindrical cap-shaped terminals after the interior of the insulating tube has been filled with the arc extinguishing substance.

2. The method as defined in claim 1 wherein at least one part of the fuse element is formed into a hollow helical configuration.

3. The method as defined in claim 1 wherein loops are formed respectively at both ends of the fuse element.

4. The method as defined in claim 1 1 wherein the depths of the plurality of slits in said circular discs are made different from each other. 

1. A method for producing electric power fuses comprising
 1. a step comprising preparing two circular discs of different diameters, each disc having a central square hole, a plurality of slits cut radially in a spaced apart relation along the periphery of the disc but not reaching the central square hole, and a plurality of lugs formed by bending the disc material outwardly at the inner bottom of each of the slits, and disposing the two discs thus prepared in an opposed but spaced apart relationship by an assembling jig having a longitudinal axis so that each of corresponding slits in the two circular discs are aligned along the longitudinal direction of the assembling jig;
 2. a step of inserting each of fuse elements into a respective pair of the aligned slits in the two discs, with both ends of the fuse element being fixed around the lugs provided at the bottoms of the corresponding slits;
 3. a step of rotating the jig intermittently around the longitudinal axis of the jig;
 4. a step of enclosing the fuse elements thus assembled within an insulating tube made of an inorganic, heat-resistant, ceramic material and having cylindrical cap-shaped terminals at both ends of the insulating tube;
 5. a step of removing the jig out of the fuse assembly after the discs and the cylindrical cap shaped terminals have been brazed together, respectively;
 6. a step of filling the interior space of the insulating tube with an arc extinguishing substance through one of the square holes which is left open after the jig has been removed; and
 7. a step comprising securing by brazing end caps to both ends of the cylindrical cap-shaped terminals after the interior of the insulating tube has been filled with the arc extinguishing substance.
 2. a step of inserting each of fuse elements into a respective pair of the aligned slits in the two discs, with both ends of the fuse element being fixed around the lugs provided at the bottoms of the corresponding slits;
 2. The method as defined in claim 1 wherein at least one part of the fuse element is formed into a hollow helical configuration.
 3. The method as defined in claim 1 wherein loops are formed respectively at both ends of the fuse element.
 3. a step of rotating the jig intermittently around the longitudinal axis of the jig;
 4. a step of enclosing the fuse elements thus assembled within an insulating tube made of an inorganic, heat-resistant, ceramic material and having cylindrical cap-shaped terminals at both ends of the insulating tube;
 4. The method as defined in claim 1 1 wherein the depths of the plurality of slits in said circular discs are made different from each other.
 5. a step of removing the jig out of the fuse assembly after the discs and the cylindrical cap shaped terminals have been brazed together, respectively;
 6. a step of filling the interior space of the insulating tube with an arc extinguishing substance through one of the square holes which is left open after the jig has been removed; and
 7. a step comprising securing by brazing end caps to both ends of the cylindrical cap-shaped terminals after the interior of the insulating tube has been filled with the arc extinguishing substance. 